Windfarms

Ad Hoc Marine Designs have been engaged within the Windfarm industry for several years in varying roles from designing windfarm boats through to general advice and consultancy of feasibility projects. John Kecsmar sits on many committees including the MCA’s High Speed Advisory Group which deals with the issues of the high speed industry from a designers, and legislators perceptive and the RINA HSV committee. John also sits on Lloyds Register Technical committee, serving a similar role as the HSCAG and is the current chairman of RINA’s High Speed Vehicle Committee.

Being on these committees and working close with Flag and Class, we have developed a better understanding of the needs of this growing industry. The formulation of new rules and regulations have enabled us to ascertain the direction the industry may take and can therefore advise on the latest developments.

Having designed several Windfarm boats and also unique methods of transfer of windfarm technicians from the vessel to the turbine we have established very good relationships with several operators of these boats as well as the problems being encountered on a daily basis. This in-depth knowledge provides us with a very clear picture of what is required, and as such, are able to tailor designs and technical advice with greater satisfaction to our clients.

Windfarm Service Vessels

Whatever claims are made by the builders/operators for the seakeeping of the current range of catamarans for wind farm servicing there is little doubt that these small craft 15m to 24 m long have limitations when it comes to meeting head seas in particular. Speeds of 25 knots are mentioned. Significant wave heights of 2m are also mentioned. But the reality is that the two numbers don’t go together. A considerable reduction of speed is enforced by the violent motion in even 1m seas. This is a problem that has plagued the researchers and designers of small fast craft for over a century- that of combining speed and seakeeping. This situation is compounded in the UK for operators of WFSV by the Load Line regulations and MCA invoking the HSC Code vessels over 20knots; see below ‘Current Scenario’ for more details.

Monohulls, deep vees, catamarans, trimarans, they have all been tried in the wind farm market. SWATH craft are also on the agenda. But they are perceived by the market to be slow and very expensive. However, Ad Hoc Marine Designs have been involved in SWATH designs for 30 years including “Patria” now “Sunflower 22″ running from Busan in South Korea, still the fastest commercial SWATH in the world at 31 knots. Other SWATHs have been the Passenger Transfer Craft used by the MOD in Plymouth UK and the Lockheed Martin SLICE crew boats delivered in 2006.

It is this knowledge that has prompted Ad Hoc Marine Designs to design a SWATH called The Typhoon Class especially for wind farm use that can really combine those magic figures of circa 25 knots and 2m significant wave height so the two figures can work at the same time, without the requirement to slow down. Additionally, the design is under the 24m Loadline restriction which over comes many regulatory hurdles. A typical General Arrangement layout of the 24m Fast Swath is shown and a brief specification & details attached. These of course can be altered to suit your own requirements.

The 26m Typhoon Class Swath has recently been independently tank tested at Haslar test tank by a private client for verification. The model was run in significant wave heights of 2.2m at speeds of 21knots in head and stern seas, free running of 25knots in Hs = 2.75m. The results indicate a very slow and benign motion. The model was then taken for free running open water test to push the boundaries of the design limits. The model was run in all sea headings from: stern to beam to quartering to head seas. And finally being pushed up against a wind turbine tower. The speed was 25knots in a Hs of 2.75m, thus beyond the design limits. The motions were benign and the model able to maintain speed in the increased sea sate with some occasional minor bow slamming, owing to the freeboard or wet deck clearance being reduced. This was expected with an ever increasing wave amplitude, and is cured simply by raising the freeboard or wet deck clearance. The bow of the model remained stationary against the turbine and the force to push is significantly lower than conventional vessels. All the results indicate the vessel meets all design parameters comfortably.

24m Fast Swath
24m Fast Swath Turbine

This particular 26m Typhoon Class of Swath is unique to the Windfarm Market. It is suitable for the heavy workboat and crew boat duties that these vessels are required to perform whilst at the same time being able to maintain a year round operability. A SWATH not only has significantly lower motions, but more importantly it can maintain service speeds in ever increasing significant wave height. A larger HSC 2000 Code 29m version is shown here.

Autobrow – A unique vessel to turbine transfer system

The history of the brow’s development is highlighted by the research and development and proven in service with the first being installed on 2 SWATHs built for the UK MoD. The original Brow was a simple yet elegant concept by Nigel Warren (then chief designer) and developed within the FBM Marine (now Babcock) design team in 1997. The brow was designed to safely transfer Flag Officer Staff Training (FOST) staff from one vessel to another whilst at sea.  A special purpose SWATH Passenger Transfer Craft was designed and built at FBM Marine for the UK MoD with a Brow system for passenger transfer. A Swath was selected owing to its benign motions compared to conventional multihull vessels. Further details of the SWATH and Brow system may be found in “Designing a Special Purpose SWATH to the HSC Code” by Warren. N & Rudgely G. The Safety of High Speed Craft RINA Conference in 1997 and “Revisiting a SWATH Design 7 Years On” by Warren N., Kecsmar J. SURV 6: Surveillance Pilot & Rescue Craft RINA Conference in 2004.

The brow is essentially a platform that has vertical and horizontal modes of translation via hydraulic cylinders. The brow was sited on the side of the Swath thus rotation motion such as roll translates into a vertical motion similarly with pitch and of course pure heave. Below are images of the Swath and Brow system in action (images curtsey of D.L.O.).

 

 

A second more extensive Brow was designed by Ad Hoc Marine Designs for Lockheed Martin in 2007/8. The purpose of the brow, as the original, is to transfer personnel from ship to platform, however this time for the offshore Oil industry.  As in the original brow, the vessel is sited on a SWATH, thus making the periods of motion considerably easier to overcome. Owing to the extensive safety requirements the size of the brow increased to accommodate all the range of motions and possible collision/impact scenarios. Two different solutions emerged one being in aluminium, the other in composite. Extensive FEA and model testing was conducted.

 

Ad Hoc Marine Designs Ltd. is one of thirteen finalist of the Offshore Wind Accelerator (OWA) – Carbon Trust competition to develop a safe transfer system. The patent pending winning design by Ad Hoc Marine Designs is called the Autobrow and is being project managed to satisfy OWA’s requirements by Otso.

Having previously designed 2 successful transfer systems noted above the experience gained from these were employed into this new design.  The challenge being to compensate for the higher motions of a small multihull rather than a SWATH. The system is intended to allow technicians to transfer more safely onto windfarm towers than is currently possible and also in seas with a significant wave height of up to 2.5m.   Depending on the motion of the vessel on which the brow is fitted up to 3m significant wave height should be achievable. Installation of the Autobrow onto Ad Hoc’s 26m Typhoon Class Swath is an ideal combination, as the swath design experiences approximately one quarter of the vertical motions of a conventional catamaran thus allowing the maximum range of excursion. With Ad Hoc Marine Design’s expertise in aluminium design and fabrication coupled with FEA investigating many “what if” scenarios, an updated brow was designed to cater for the higher laods.

 

The Autobrow has been designed to satisfy requirements of the Carbon Trust and the existing WFSV that are currently operating in the EU waters. However, should your requirements differ, such as size of vessel or range of motions etc then Ad Hoc Marine Designs can redesign the brow for your exact requirements. Please contact Ad Hoc Marine Designs using the contact page.

Ad Hoc Marine Designs has since developed another variant for crew transfer. Its principal aims are as before, yet without the onerous deck space envelope currently employed. Sub 24m vessels are extremely deck space limited and without a large working deck the multitasking of such Windfarm vessels become limited. The need for a compact yet effective solution remains. Thus model testing of the sytem is aimed to begin in the autumn 2014 in order to perform proof of concept. Details shall be released upon final testing.

Swath Designs for Different roles:

In the Gallery is also shown more variations of the Typhoon Class of Swath designed by Ad Hoc Marine Designs. These range from 15m up to 50m and speeds from 12 knots up to 30 knots. More details upon request.

Additionally, we have given a brief description of some of the problems that currently face the Windfarm industry. This has been printed in the August 2010 edition of Work Boat World.

An excerpt from the WBW article is given below:

Current scenario

Offshore wind farms are sprouting up rapidly in European waters around the shores of the UK, Denmark, Germany and several other countries. In order to assist with the construction and maintenance of these turbines a large number of small vessels are in operation mainly to take technicians and small items of equipment out to the site. Time is money so the vessel’s speed is of the essence. The industry is developing fast but the ideal type of boat has not yet been developed. Reliability is important, not just in terms of machinery but also in the ability of the boats to get the technicians in a degree of comfort out to the turbines and then transfer them to each wind tower safely, and back again. The ability to cope with various seastates is therefore of prime importance. Currently all shapes and sizes of craft are in service, monohulls, catamarans and trimarans, all diesel powered some with jet propulsion and some with propellers, fixed pitch and controllable pitch.

The lengths vary from about 10m to about 20m, and they carry up to 12 passengers and can do around 20 to 28knots generally. Predictions show that there will be thousands of these vessels built in the next few years.

The wind farm sites are gradually spreading further from shore into deeper and rougher waters and there is a demand for more speed, greater ability to operate and transfer in rougher water and also to carry more passengers. This inevitably means that the boats will get bigger and more sophisticated. For instance the current method of transfer of the technicians onto the ladder provided by most wind tower providers is for the boat to nose up against two vertical bars and apply up to full power to maintain position. The technician then steps off the bow onto the recessed vertical ladder and climbs a few metres up to the tower.

Naturally these craft have to be certified to operate. In the UK the code of safety usually applied is the Small Commercial Vessel code of safety. This is a sensible well developed code that allows up to 24m Loadline length, 12 passengers or 1 tonne of cargo. It allows practical and inexpensive construction and operation and categorises operation in 6 different distances from a safe haven from 3 miles to unrestricted. Speed is not an issue. There is no stipulated seastate in which the boat can operate- it’s up to the master. There is no legal requirement for the design or build to be approved by a Classification Society.

The Problem

Energy providers are becoming more demanding as their scope increase. Classification is being asked for, bigger seastates, more passengers and less passage time etc.

Energy providers who construct and operate these windfarms contract out their requirements to windfarm boat operators, in parcels. Anywhere. So these boats may have to operate out from different ports in Europe not just the UK at any time. Other countries flags have different technical requirements and modifications may have to be made (if possible) before a boat can operate in (say) German waters. There is no uniform code.

This situation is hard enough when the boats are less than the SOLAS 24m rule, and carry less than 12 passengers- also a SOLAS criteria. And if the speed is more than 20 knots this can be an issue invoking the SOLAS HSC Code.

Current policy in the UK is that if a boat carries more than 12 passengers and it is faster than the speed criterion stated in the HSC code, then it must meet the HSC Code. The speed criterion is related solely to displacement and even a 100 tonne boat will be HSC if it can do more than 15 knots. The HSC Code was principally devised for fast passenger/car ferries carrying hundreds of fare paying passengers whether disabled, elderly or a child (not counting babies under one year old). See figure for principal differences between the SCV and HSC code.

So there are three problems:-

  1. Under 24m/12 passengers. Lack of uniformity in the EU flag states.
  2. A bigger problem is if the EU flag state demands Classification.
  3. An even bigger problem is if the craft is more than 24m/12 passenger (‘passengers’ in SOLAS definition of word) and over 20knots.

Wind farms at sea, from the air

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